The present invention generally relates to the electronic clearing of yarn, in which the yarn passes through a measuring head that scans its cross-section and provides corresponding cross-section signals, and wherein deviations of these signals from given clearing limits are established so that those yarn faults can be cut out of the yarn when the signals exceed the clearing limits of one or more quality criteria. By the same token, the invention relates to the quality assessment of yarns by detecting yarn faults according to several criteria, and determining their respective numbers, for the purpose of establishing the clearing limits of a yarn clearing system, as well as the classification of uncleared and cleared yarns.
In one method of yarn clearing carried out in the USTER CLASSIMAT System, described in the Uster News Bulletin No. 29, August 1981, yarn faults are classified according to length and cross-section into a total of 23 classes for short thick places, double threads, long thick places and long thin places. With the aid of USTER KORRELATOR stencils, values for clearing parameters (i.e. reference length and sensitivity) are determined from the CLASSIMAT results taking users' requirements into consideration. The corresponding values for the fault cross-section, i.e. sensitivity, and for the reference length, which is the length over which the mean value of the yarn cross-section is formed, are set in a yarn clearing device. Thereafter, those faults which exceed the limits established by the chosen values are cut out of the yarn and replaced by a knot.
It is a fact that the cleared yarn still has yarn faults, to be precise those which were categorized as tolerable in the clearer setting. Thus, in respect of these non-cleared yarn faults, as well as the fact that a substantial number of yarn defects are actually caused by irregularities that are proper to the spinning process, there may be differences in quality between different bobbins of cleared yarn. However, such a difference in quality may also exist in relation to other parameters, such as, for example, the number of splices or knots, the number of neps, or the coefficient of variation of evenness (CV%). Additionally, there is also a difference in relation to the yarn fault classes used in the USTER CLASSIMAT.
The fact that two bobbins cleared by the same clearer and at the same setting generally may not have the same quality leads to the consideration that it is desirable for a yarn manufacturer to be able to differentiate between bobbins of cleared yarn according to quality criteria. This would indeed open up the interesting possibility of being able to provide branded products of different levels of quality, to thereby be able to sell the higher-quality products at better prices.
A qualitative differentiation of yarn bobbins cleared according to the same clearing parameters, on the basis of the results of an on-line classification into a plurality of yarn fault classes or on the basis of the CLASSIMAT classes or a similar scheme is, however, relatively complex and, additionally, not very meaningful in terms of textile technology. Indeed, since the coarse faults are cleared out in any case, only a few definitive CLASSIMAT classes remain. If, however, only a few classes are relevant, a disproportion results between the technical effort required for complete classification and its potential result. An additional factor is that, with only a few classes, the scope or range of possibilities is poor since the "quality pattern" related to the few classes is too rough.
It is therefore an objective of the invention to provide a novel method which permits a definitive and reproducible qualitative differentiation and classification of electronically cleared yarn, while using the least possible expenditure in terms of technology and cost.
It is another objective of the invention to provide a novel yarn clearing method and apparatus which is more efficient and more flexible and also less cumbersome to determine optimum clearing limits compared to the method traditionally used with the USTER CLASSIMAT system.